The present invention relates to a method and apparatus for a solar power conditioner, and more particularly, to a method and apparatus for enhancing DC to AC power conversion in synchronized power utility distribution grid conditions.
The electrical utility industry is presently, and has for some time, labored under the problem of supplying cost-effective power to comply with system peak-demand period requirements. Moreover, our nation""s energy demand requirements, especially at peak-demand periods, continue to grow each year. The world at large has an even larger problem since emerging industrial nations require energy to fuel their economic development. This has presented a problem since it is neither financially nor environmentally practical to construct the necessary nuclear or fossil fuel generating plants that would operate at 20% capacity, or less, during less than peak-demand periods. Thus, a means by which electricity can be economically generated is an immediate requirement, especially one that can lend itself to supplementing peak load requirements by an environmentally clean means.
The concept of peak-demand power supplementation is not new. Indeed a number of systems have been tried and implemented over the years, based mainly on batteries, hydroelectric, and combustion turbine or engine schemes. For example, installations using the following have been tried:
1) Storage batteries which store rectified AC power during periods of low demand;
2) Auxiliary oil-fired plants;
3) Wind generation;
4) Hydro-electric;
5) Small, medium and large capacity kerosene/natural gas turbines; and
6) Solar energy.
Each of the above, either by nature or by implementation, has had problems to date. Some are expensive, others are not acceptable environmentally, some pollute, some are ugly and require lots of space, and some require extensive human attention. Solar systems which have attempted to capitalize on solar energy have been, to date, either too expensive, occupied too much space, have not been aesthetically acceptable, are too inefficient, and/or have deviated too much from the electrical utility secondary distribution standards.
Furthermore, many of the above power systems require the use of an inverter in order to convert direct current (DC) to alternating current (AC). Over the years inverters have progressed from electro-mechanical to thermionic and on to state of the art semiconductor devices. At all stages the aim has been to translate 100% of the DC current into AC current. Earlier inverters used various electrical or electronic means to attempt this. These means can be summarized, for example, as follows:
1) Motor generator sets;
2) Electro-magnetic synchronous mechanical switches;
3) Thermionic tubes (Triode);
4) Thyratrons;
5) Transistors;
6) Silicon controlled rectifiers (SCR);
7) Triacs;
8) Field effect transistors; and
9) IGBT (insulated gate bipolar transistors).
Implementation of the various technologies remained fairly simple in concept and few had the inherent ability to accurately phase synchronize to a reference AC supply.
To date, grid connected, alternate electrical energy generators involving DC to AC production were normally confined to xe2x80x9cfieldsxe2x80x9d of photovoltaic arrays (solar farms) or wind farms. The size of such installations was normally greater than 5 kilowatts, with 50 to 100 kilowatt and higher installations commonplace. Converting DC energy into utility grade power required large, bulky and expensive equipment and components, which required close monitoring. Such systems were relatively inefficient with best peak efficiencies only in the 80% range.
Today, because of de-regulation of the electrical generation and distribution industry, and with the nations utilities seeking to implement distributive and/or end-of-line generation, as well as the administration""s xe2x80x9cMillion Solar Roofsxe2x80x9d initiative, there is a need for a small, efficient, low cost power conditioner inverter. Such a conditioner would be less than 5 kilowatts in size, with designs that are supportive of cost-effective mass production to achieve enhanced power economics. An inverter as such, presently used in large installations, just inverts, or changes DC power into AC power for isolated electrical loads. Such power has to be further conditioned before it can be interconnected with the utility secondary distribution grid. Employing such means further reduces the overall efficiency of the conversion system. Additionally, such systems utilize analog circuitry, which suffers from performance repeatability problems, thermal stability difficulties, reliability, and poor control of main parameters.
Accordingly, the present invention provides a method and apparatus for a solar power conditioner capable of supplying electrical power to supplement power, especially during peak-demand periods, generated by an electrical utility. The power supply generated by the electrical utility is monitored through the use of digital signal processing methods, and when needed, supplemented by power generated by solar panels.
Monitoring of the AC power from the electrical utility is accomplished by a central processor (CPU) of the solar power conditioner. The AC power is first digitized by analog-to-digital converters, which digital signal is then used by the CPU to monitor the AC current, voltage, power and phase. Simultaneously, DC power supplied by the solar panels is converted to AC by a pulse width modulator, digitized by analog-to-digital converters and also monitored by the CPU of the solar power conditioner. The CPU matches the generated power of the solar panels to that of the main supplied power by determination of each powers"" characteristics and through control of an active filter which reconstitutes the pulse width modulated signal. The CPU further controls a circuit breaker to determine when the power supplied by the solar panels will be used to supplement the AC power generated by the electrical utility.
The present invention, including its features and advantages, will become more apparent from the following detailed description with reference to the accompanying drawings.